Rapid Beeping at Startup

Hello, I am using Windows 7 Pro on a Dell Inspiron 1520. Today, when I attempted to start the unit, I heard a rapid beeping that was uncontrollable until I clicked the Control Key. There are no error messages. I have done 2 cold boots and a memory diagnostic (which found no errors) with no positive results. It begins right when the screen indicates it is Starting Windows. Once I get past that, it seems to operate normally, but I am concerned there is a root problem that will surface with disastrous results at a later time. Any suggestions, thoughts or ideas are greatly appreciated.

It' hard to say....I can hear breaks in the tone, but for all intents and purposes, it is a long, steady stream which is unintelligible in order to determine what error code it is sending. It almost sounds like one, long beep as if a key were stuck (but this is not the case). The ONLY way to stop it is by hitting the Control key. But as far as determining any pattern - not possible.

I have taken the keyboard off before, but unfortunately it is made in such a way that there literally is no way (or reason) to clean it other than with air and cleaning the buttons from fingerprints. However, I took a shot and tried Safe Mode, and the Control button did nothing to eliminate the sound. I just restarted in normal mode and again the Control button worked. I'm not sure that sheds any light, but I thought it was worth mentioning.